Professional activity, personal enmity and 'Russian trail' are possible theories of journalist Pavel Sheremet's murder in Kyiv that are being considered in the preliminary inquiry, advisor to the Ukrainian interior minister Zoryan Shkiryak said.

"Of course, this is a premeditated, cruel felony. Main theories have been spelled out. First of all, professional activity of the journalist," Shkiryak told the press at the incident scene in Kyiv on Wednesday.

A theory of personal enmity between Sheremet and unknown persons is not ruled out either, he said. "This theory is always suggested; we cannot rule out anything," he said.

The interior minister's advisor supported the opinion of his colleague, deputy Anton Gerashchenko that 'Russian trail' could not be ruled out in that crime either.

"[...] We cannot rule out the involvement of Russian security services in that crime [the explosion of Sheremet's car]," Shkiryak said.